It offers “a common install base” — Red Hat Enterprise Linux — for the scientific community, which reduces/eliminates duplication of effort, and can be customized by end users to meet specific needs. SL 4.5 is rebuilt from the source code of Red Hat Enterprise Linux 4 — more specifically, according to the release announcement, “based on the rebuilding of RPMS out of SRPMS’s from Enterprise 4 AS, including Update 5.”